Compact sewage treatment apparatus

ABSTRACT

A compact, compartmentalized sewage treatment apparatus housed in a single tank having a length appreciably greater than its height in which sewage discharged into the apparatus is progressively clarified by anerobic bacterial decomposition, primary sedimentation and flotation, chemical attack to reduce coliform bacteria and BOD, and secondary sedimentation, flotation and filtration to highly clarify the effluent for discharge into lakes, rivers, harbors and other water courses.

United States Patent Wetzel 1 1 Oct. 31, 1972 [54] COMPACT SEWAGETREATMENT 3,347,784 10/1967 Kappe ..210/195X APPARATUS 3,407,935 10/1968Burton ..210/17 X 3,451,552 6/1969 Carlson ..210/152 [72] Invent3,472,390 10/1969 Pall et a'l. ..210/152 x [73] Assignee: James R.OConnor, Arlington,

Mass. a part interest Primary Examiner-Reuben Friedman AssistantExaminer-Thomas G. Wyse [22] 1 1971 Attorney-James R. OConnor [21]Appl.No.: 200,160

[57] ABSTRACT [52] U.S. Cl. ..210/152, 210/199, 210/205 A compact,compartmentalized sewage treatment p- [51] Intel ..C02b 3/06, C02c 5/06paratus housed in single having a length 1 [58} Field of Search..210/16, 17,61,62, 152, 195, preclably greater than its helght in whichsewage 210/199, 205, 209 discharged into the apparatus is progressivelyclarified by anerobic bacterial decomposition, primary sedimentation andflotation, chemical attack to reduce [56] References cued coliformbacteria and BOD, and secondary sedimenta- UNITED STATES PATENTS tiOn,flotation and filtration to highly clarify the ef tfd'h 'tl,',hb2,988,221 6/1961 Culp ..2l0/62X 35 akes "Vets and 3,202,285 8/1965Williams ..210/195 3,327,855 6/ 1967 Watson et al. ..210/152 X 21Claims, 3 Drawing Figures PATENTEDnma; I922 6 FIG.3

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to sewage treating apparatus of the type generally found in U.S.Art Class 210 titled Liquid Purification or Separation and moreparticularly to apparatus of a compact and frequently portable naturefound in Subclass 199 subtitled With Means to Add TreatingMaterial-Spaced Along Flow Path.

2. Brief Description of the Prior Art The development of the inventiondisclosed herein was principally motivated by the recognition of theneed for a sewage treatment apparatus particularly adapted for use insmall marine pleasure craft equipped with marine toilets. That is not tosay that the invention might not find ready application in otherinstallations wherein space limitations are critical or even in largercraft which are not equipped with a central sewage treatment apparatus.The merits of the invention will be best understood, however, byconsidering same in the frame of reference of its adaptability for smallpleasure craft installations.

Smaller craft of course frequently sail inland waterways, to wit, lakes,rivers, harbors, bays, and the like water courses. In the past, thepractice has usuallybeen todischarge sewage from marine toiletsoverboard and this practice has contributed in no small measure to thedeplorable condition of our domestic waterways which presently exists.To rectify this condition, both federal and state environmentalprotection agencies have sought or will increasingly be seeking theenactment of legislation which will prohibit the dumping of untreated orraw sewage overboard and such legislation will no doubt be enforced by,among other measures, denial of registration by regulatory agencies toany craft which is not equipped with sewage treating apparatus.

It has also been a more limited past practice to utilize on board sewageholding tanks which stored sewage for a limitedperiod of time andrequired frequent pumping out at dock side into municipal or privatesewage systems and treating plants. Notwithstanding this inconvenience,which does not particularly recommend storage tanks to pleasure craftowners, space limitations severely limit the size of such tanks (thusrequiring more frequent pumping or emptying), the tanks present a safetyhazard particularly if they must be installed below the water line,i.e., they are generally not acceptable to regulatory agencies such asthe Coast Guard, and it is highly unlikely that they will satisfyenvironmental protection agencies in that sewage stored in tanks whichcan be mounted in smaller craft can'be readily dumped overboard from thetanks into water courses by those who would violate antipollution laws.

ln view of the continually increasing public interest in'and demand foreffective water pollution controls, it is not surprising to learn thatothers have in recent years recognized the need for sewage treatmentfacilities in smaller boats and other installations wherein space formounting same is limited. One individual who has is Mr. Rollin L. Fiferof Louisville, Kentucky, to whom US. Pat. Nos. 3,460,677 and 3,476,250issued in 1969. Reference may be had to Fifers patents for a furtherdetailed explanation of the need for sewage treating systems in smallercraft and the disclosure of a relatively small, compact unit having alength in excess of its height and width which is suited for the type ofinstallations under consideration. While I am not aware of any presentcommercial usage of the apparatus disclosed by Fifer, I believe it isonly fair to recognize that he has made a meritorious contribution tothe art, particularly with respect to the compactness of his device andhis teaching that the length of the apparatus must exceed it height andat the same time function as efficiently or even more efficiently thanpreviously known treatment systems in order to be acceptable for smallcraft utilization.

Thus, while recognizing the significance of Fifers teachings, it is theobject of this invention to provide a still fiuther improvement in theart. To that end I have developed a sewage treatment apparatus which:(a) is of such compact size as to be practical for usage aboard craft assmall as 20 feet in length; (b) relies solely on the force of gravity toinduce effluent flow; (c) is mechanically simple in that it has nomoving parts per se (Fifers apparatus requires a system of pipes,valves, manifolds and presumably a pump or compressed air source tocontinuously inject air, i.e., oxygen, into a desired circulationpattern in his tank), and thus is particularly conductive for economicproduction and sale in the market for which it is intended; (d) isdesigned to achieve almost complete separation of solids and liquidsduring flow of effluent through the apparatus to effect a verysubstantial reduction of BOD, (Fifer by comparison makes almost noattempt to separate solids, but to the contrary specifically seeks tokeep solid matter continuously in suspension); (e) provides for aconcentration of heavier solids in a holding tank wherein anerobicdegradation of the sewage is effected, (Fifer by comparison reliessolely on aerobic bacterial, action); (f) provides forthe filtration ofeffluent flowing downstream from the above mentioned holding tank, thechemical treatment of relatively clear, previously filtered effluent,and further separation of solids and liquids in the chemically treatedeffluent by settling, flotation and subsequent filtration processes toeffect neutralization of coliform bacteria and a very substantialreduction of the BOD of effluent prior to discharge. Conversely, Fiferprovides for chemical treatment only and makes little or no attempt toeffect solid separation by any of the processes of settling, flotationand filtration. Further appreciation of the contribution to the art ofthe present sewage treatment apparatus will be had by one who nowproceeds to a consideration of the detailed description of a preferredembodiment of same which follows hereinafter.

SUMMARY OF THE INVENTION A compact, compartmentalized sewage treatmentapparatus, the length of which is substantially greater than its heightand width. A single tank has a primary effluent receiving chamber in thebottom region thereof into which sewage effluent is discharged from anintake pipe. In this region of the tank heavier solids settle out of theeffluent toward the tank base and biological decomposition of theeffluent by anerobic micro-organisms takes place. In the primary holdingchamber, but above the bottom region thereof, there are a plurality ofplanar, horizontal baffles spacedly stacked above one another and havingopenings alternately disposed adjacent opposite ends thereof. The

.clarified effluent flows downstream through the said primary filters. Achemical treatment chamber is located longitudinally adjacent thesecondary holding chamber and is separated therefrom by a transverse,vertical baffle having a cut out at one end thereof providing a weirover which effluent flows into the chemical treatment chamber responsiveto filling of the secondary holding chamber. A nozzle which is attachedto the tank communicates with the chemical treatment chamber for theperiodic injection of a desired chemical solution into the effluentpresent in said chamber to effect the neutralization of colifonnbacteria and reduce the biological oxygen demand of the effluent. At thedownstream end of the chemical treatment chamber, a second transversebaffle extends across the width of the tray and'the latter baffle has anopening adjacent the base thereof communicating with the first of aplurality of settling and flotation chambers defined by a plurality ofspaced, longitudinal baffles joined to the base of the tray andextending from the downstream side of the last mentioned transversebaffle t the opposite end of the tray. Each of the settling andflotation chambers communicates with the adjacent downstream chamberthrough openings in the longitudinal baffles, which openings arealternately disposed at opposite ends of the said baffles andalternately are vertically spaced so as to be adjacent the top, bottom,top, etc., of succeeding baffles relative to the downstream flow path ofthe effluent. Each of the aforesaid openings in the last mentionedtransverse baffle and the longitudinal baffles may have a filteroverlying the upstream side thereof,.with the said filters being ofprogresssively finer mesh in relation to the downstream flow path. Thus,the settling and flotation chambers provide an extended flow path forthe further separation of solids and liquids by flotation, sedimentationand filtration during the relatively quiescent downstream flow of theeffluent. A conduit for the discharge of highly clarified effluent fromthe apparatus communicates with the upper region of the most downstreamof said settling and flotation chambers. Ideally, the apparatus mayinclude a second nozzle disposed to inject additional chemical into oneof the intermediate of said settling and flotation chambers to effect aconcentrated chemical attack on any remaining bacteria and a furtherreduction of the BOD of the already highly clarified effluent upstreamof but relatively proximate the discharge conduit.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of asewage treatment apparatus according to the invention depicting portionsof a side, cover and end of the tank removed and in section, andportions of certain internal components of the apparatus removed;

FIG. 2 is a cross section taken on line 2--2 of FIG. 1; and

FIG. 3 is a cross section taken on line 33 of FIG. 1.

DESCRIPTION OF 'A PREFERRED EMBODIMENT A typical sewage treatmentapparatus according to I the invention comprises a generally rectangulartank 2 having a base 4, upstanding sides and ends 6,8 respectively, anda removable cover 10. As depicted in FIG. 2, base 4 maybe slightlyslopedtoward one end 8 of the tank. A normally capped pipe 9 leads intothe tank adjacent the bottom of its left end 8. The pipe 9 is adaptedfor connection to a hose to facilitate the periodic pumping out of anysludge collected on the base 4 or for complete emptying of the tank toeffect periodic,

e.g., annual, semi-annual, etc., cleaning of the apparatus according tothe extent of its usage. While the external dimensions of the tank mayvary as the demands of a particular installation dictate, experience todate has indicated that a unit for handling the eflluent from a marinetoilet installed in a boat with accom modations for four persons to liveaboard can be as small as 30 inchesX16 inchesX16 inches under relativelynormal usage conditions. A unit to handle the toilet effluent for twopersons can be as small as 26 inches l2 inchesXl2 inches. In any event,it is highly desirable or even imperative that the length-to-heightratio of a unit acceptable for small craft installations be greater thanone. The tank must of course be fabricated from an impervious material,ideally a lightweight, corrosion-resistant synthetic plastic. In fact,it has been found that all the components of the apparatus particularlylend themselves to manufacture from synthetic plastics, by molding,laminating, extruding, weaving, etc.

The inside of the tank 2 per se is hollow and for the purpose of thisdisclosure the bottom region thereof is referred to as the most upstreamregion of the apparatus and the tank. This bottom or most upstreamregion of the tank defines a primary holding chamber 12 the top or mostupstream region of which is defined by the base of a tray seated in thetank, which will be described in detail hereinafter. Intermediate theheight of the primary holding chamber 12, three planar, generallyhorizontal, vertically spaced baffles 14 extend between the internalwalls defined by the sides and ends of the tank. Horizontal baffles 14are fixed to and supported in vertically spaced relationship by supportelements 18 which project inwardly from the end walls of the tank.

An effluent intake pipe 19 which is connected to the discharge line ofthe marine toilet extends through an appropriately sized opening in thecover 10 of the tank, through the base of the aforementioned tray,through the longitudinal baffles and terminates below the baffles butabove the base of the tank, whereby sewage effluent from the toilet isinitially discharged into primary holding chamber 12 at substantiallythe most upstream region of the apparatus. As the primary holdingchamber fills, heavier solids in the effluent will settle out ofsolution onto the base 4 of the tank and air (oxygen) or other gasseswill rise upwardly out of the chamber toward the cover 10 of the tank.This purging of air from the lowermost region of the apparatus createsthe ideal environment for continuing digestion and decomposition of thesewage in this region by anerobic bacteria which are of course highlyactive in a limited dissolved oxygen environment. Thus, initialtreatment by way of separation of solids and liquids and reduction ofBOD by anerobic biological degradation of organic matter present in theeffluent is effected in the lowermost region of the primary holdingchamber 12.

Early in the development of the apparatus, it was recognized thatconditions peculiar to the marine environment in which it would beutilized would precipitate turbulence in the primary holding chamber 12thus creating a counteraction to the settling action desired to effectprimary separation of solids and liquids in the said chamber. Tominimize this adverse effect of turbulence and for other reasons to bedetailed hereinafter, the longitudinal baffles 14 were incorporated inthe apparatus. As is best seen in FIG. 1,

and is further indicated by the flow path arrows in FIG. 2, each of thehorizontal baffles has a plurality of spaced apertures disposedproximate one end thereof and at opposite ends of vertically adjacentbaffles. This arrangement of the apertures 20 provides for an extendedflow path of partially clarified effluent upwardly or downstream fromthe lowermost region of the primary holding chamber. One will observethat the area defined by the openings 20 constitutes only a minorportion of the overall area of each baffle and that each opening per seis relatively small. Hence, while some solid particulate matter willpass through the openings, larger flocs will be inhibited from passageand will be retained in the lower settling chamber for furtherdecomposition thereof. It will also be noted that the vertical spacebetween the baffles is quite limited so as to provide for quiescent flowalong the extended path and further minimization of the effects ofturbulence. Additionally, while anerobic bacterial action will continueas the effluent traverses the extended flow path, the aforementionedrelative quiescence will enhance additional settling of solids onto theplanar surfaces of the battles. Having recognized that this additionalsettling will occur, it was determined to be advantageous to mount thebaffles so that each would slope slightly downwardly (see FIG. 2) fromthe horizontal toward the apertured end thereof and the base of thetank, whereby solid particulates settling out would tend to slidedownwardly and drop back through the apertures 20 of the respectivebaffles and ultimately back into the holding chamber 12. The objectiveof course is to realize maximum liquid-solid separation and thus producea substantially clarified, relatively solid-free effluent flowingdownstream in the flow path above the uppermost of the baffles 14. Tothis end it has been further recognized that light eddy currents in theeffluent and/or mild vibration of the longitudinal baffles induced bythe normal pitching and rolling of a small craft will tend to agitatesolid particulates settling onto the planar surfaces of the baffles andthus enhance the sliding descent of such particles toward the chamber12.

The earlier mentioned, generally rectangular tray or subassembly 21?; ismounted within the tank above the baffles 14 and includes a base 24seated on support elements 26 projecting inwardly from the end walls 6of the tank, and upstanding sides 28 and ends 30 which terminateproximate the undersurface of the cover 10 of the tank. As is best seenin FIGS. 2 and 3, the tray is narrower and shorter than the internalwidth and length of the tank, ergo its ends 30 and sides 28 are slightlyspaced from the internal end and side walls of the tank. The spacing ofthe tray from the tank provides a perimentrical gap about the traythrough which gases may escape upwardly toward the tank cover from theprimary holding chamber 12, which. gases are ultimately vented to theatmosphere overboard of the craft through effluent discharge line 32.

The components of the apparatus housed within or supported by the tray22 will now be described in essentially a right to left sequence asviewed in the drawings, which direction corresponds relatively to thecontinuing downstream flow path of the sewage effluent. Spaced a desireddistance longitudinally from the right end 30 of the tray 22, thedistance being determined by the overall size (particularly the length)of the apparatus, is an impervious transverse baffle 34 which extendsbetween the sides 28 of the tray and from the base thereof upwardlygenerally to the height of the sides, except for a small section towardthe remote side of the tray (as viewed] in FIG. 1) which is of slightlyreduced height to provide a weir 36, the pur pose of which will later bedescribed. Transverse baffle 34 cooperates with the rightward end andside portions of the tray to define a secondary effluent holding chamber38 downstream of the primary chamber 12.

Mounted in the base of the secondary holding chamber 38 are a pair ofshort generally tubular extensions 40 which extend through appropriatelysized openings in the tray base in an air and liquid tight fittingtherewith. As is best depicted in FIG. 2, the extensions 40 extend bothabove and below the level of the tray base 24. Primary filters 42 arefixed to the lower or most upstream ends of the extensions 40 so as tolie intermediate the underside of the tray base and the upper surface ofthe uppermost horizontal bafile 14. Since, as aforesaid, there will besome settling of heavier solid particulates out of efiluent solutiononto the uppermost horizontal baffle 14 and further, since there will besome flotation of lighter particles upwardly to the lever of theundersurface of the tray base 24, the positioning of the filters at thelower ends of the extensions 40 has the effect of locating the filterscreens in the environment of the most substantially clarified effluentflowing downstream of the tortuous path defined by the horizontalbaffles.

The filters 42 are ideally screens of single layer, woven monofilamentof mesh openings in the range of 0.0004-0.0l0 inch. Screens of this typeutilized in prototypes of the apparatus constructed to date have provedhighly efficient in preventing passage of particulate solid matterlarger than their pore size and in combination with the earlierdescribed horizontal baffies comprise a system which will effectivelyremove over percent of the solids from sewage effluent that passes thisstage in the apparatus. In addition, the direction of efiluent flow,i.e., upward with the upstream surface of the filters located on thebottom or underside thereof, facilitates automatic cleaning ofaccumulations of nonpassing solids from the filters by virtue of gravityand the normal turbulence common to the marine environment. Further, thefilter screens are rendered nonclogging by virtue of the properselection of filter screen area in relation to the maximum flow rate tobe expected. It should be pointed out that while a pair of screens aredepicted in the accompanying drawing, the number may be increased asdesired depending upon the size of the apparatus and the work loadexpected to be imposed upon it. Typically, a filter screen area on theorder of 65 sq. inches will function satisfactorily at a maximum flowrate of three gallons per hour which is equivalent to six to eightflushes of a marine toilet during that time span. It is also critical toefficient functioning of the filters that the apparatus be provided withmeans for degassing the holding tank 12. Those familiar with filteroperation will readily recognize that the filter screens, howeverpermeable they may be to liquids and solids smaller than screen poresize, will be quite impermeable to gas when submerged in a liquid asnormal operation of the present apparatus requires. Thus, as aforesaid,to provide for the purging of gases upwardly from the chamber 12 andultimately overboard through discharge line 32, the tray 22 isperimetrically spaced from the internal side and end walls of the tank.Additionally, the use of multiple filter screens and the location ofsame appreciably below the base of the tray further reduces thepossibility of the formation and entrapment of gas bubbles at theunderside of the screens andv contributes to efficient functioning ofthe system unhindered by air or gas lock.

The filling of primary holding chamber 12 and subsequent flow ofeffluent through primary filters 42 results in an ultimate filling ofsecondary holding chamber 38 and the progressive downstream flow ofhighly clarified, i.e., substantially solid-free effluent over weir 36into the chemical treatment chamber 44, the downstream end of which isdefined by a second transverse baffle 46 extending upwardly from thebase 24 and between the sides 28 of the tray 22. Periodically, ideallycoincident with each flush of the marine toilet, a measured amount of anappropriate chemical, for example, an acqueous solution of sodiumhypochlorite is injected into the chamber 44 through nozzle 48 and theline 50 which leads to the tank from a chemical holding reservoir. Todate it has been found convenient and efficient to utilize a simple,commercially available hand operated pump having a plunger which isdepressed by the toilet user to force a predetermined (according toplunger setting) amount of chemical from the reservoir into the line 50and the treatment chamber immediately after each toilet flush.

The total effect of the chemical is to neutralize all coliform bacteriain the sewage effluent, and, by reacting with the dissolved organicmaterials in the sewage, to reduce the BOD of the effluent to a safelevel prior to discharge from the apparatus. To enhance theeffectiveness of the chemical attack and reaction, it was founddesirable to retain the chemically treated effluent in the apparatus foran extended time. To this end, the apparatus is provided with meansdefining an extended flow path for the efiluent downstream of thechemical mixing chamber 44 and transverse baffle 46 toward the enteringend 52 of the discharge line 32. The said means comprises a plurality oflongitudinal baffles or gates 54 which are laterally spaced apredetermined distance from one another and the sides 28 of the tray,and extend upwardly from the base 24 of the tray and between thedownstream side of the baffle 46 and the remote or left end 30 of thetray. Baffles or gates 54 cooperatively with each other and the sides ofthe tray thus define a plurality of settling and flotation chambers 56.

The first of the chambers 56, i.e., the forward most chamber as viewedin FIGS. 1 and 3, communicates with the chemical treatment chamber 44through an opening 58 located adjacent the base and forward end oftransverse baffle 46, each of the succeeding chambers 56 communicateswith the next downstream chamber through openings 60 disposedalternately at opposite ends of adjacent baffles and alternately invertically spaced relationship at the top and bottom of adjacentbaffles, and the last or most downstream of the chambers communicateswith the entering end 52 of the discharge line. The downstream extendedflow path I of effluent through the chambers 56 is clearly depicted bythe alternately oppositely directed arrows at the left portion of FIG.3.

In addition to providing an extended time for chemical reaction, thechambers 56 further enhance clarification in that additional settlingand flotation of solids out of solution in the effluent will take placeduring downstream flow along the extended path. As is best seen in FIGS.1 and 2, the openings 58, 60 in each of the baffles 46 and 54,respectively, have a fine mesh filter screen 62 overlying the upstreamside thereof and each of these secondary filters becomes progressivelyfiner i.e., the pore size is reduced, relative to the downstream flowpath. This secondary filtering action retains very fine solidparticulates in the environment of the active chemical on the upstreamside of each of the screens until the chemical action has reduced theirsize sufficiently to permit passage through the respective successivescreens in the downstreamward sequence. Time delay for the passage of agiven particular sewage slug through the chemical treatment portion ofthe apparatus is related to the number of toilet flushes per day, ergothe capacity of the treatment chamber 44 and the length of thedownstream extended flow path should ideally provide for an averagereaction time in the range of eight to 24 hours for a given boat sizeinstallation.

Having reference to FIG. 1 in particular, the reader will observe thatthe end of line 50 which leads back to the chemical reservoir isequipped with a second nozzle 64 of somewhat smaller diameter than thenozzle 48 and defines with the first nozzle an inverted T or Y at theterminal end of the line 50. Through this secondary nozzle a lesseramount of chemical is injected into one of the intermediate of thechambers 56 simultaneously with each injection into chemical treatmentchamber 44, with the ratio of chemical divided between the two saidchambers according to sizing of the respective nozzles. This injectionof additional chemical into an already highly refined and clarifiedeffluent provides for a very substantial reduction of BOD of the sewage,in that a concentrated chemical attack is directed at any remainingdissolved organic matter after depletion of the bulk of the chemicaloriginally injected into the chamber 44. Thus, the effluent whicheventually reaches the entrance 52 of discharge line 32 is almosttotally liquid, i.e., in excess of 98 percent solid-free and the BOD ofthe effluent has been reduced over percent from that of the sewage whichenters the apparatus and to a level which is both safe for discharge andwithin the standards expected to be established under the Federal WaterPollution Control Act (Public Law 91-224; 84 Stat. 100-103).

The reader will of course appreciate that changes and modifications intheabove described preferred embodiment may and no doubt will beeffected according to the dictates of particular small craftinstallations. For example, while the number of chambers 56 depictedinthe drawing is six, that number may readily be increased to extend theflow path and chemical reaction time by adding more gates or horizontalbaffles 54. In another aspect, further experimentation may indicate thatthe transverse baffle 34 defining the downstream end of secondaryholding chamber 38 can be eliminated without adversely affecting thefunctioning of the apparatus. At the present time the inclusion of thatbaffle to separate chemically treated effluentfrom the upstreamnon-treated effluent is considered desirable, in that the separationtends to inhibit the passage of chemical back through the primaryfilters into the lower holding chamber 12, which occurrence might wellinterfere with the anerobic degradation process since the chemical wouldkill active organisms sustaining bacterial action. However, it isrecognized that further refinements in the invention might later renderthis possibility remote. It is also envisioned that chemicals in apowdered or substantially solid form might periodically be placed in thechamber 44 in lieu of injecting same into the chamber in a liquid form.Thus, it is submitted that the reader should consider the forego ingdescription in an illustrative rather than a limiting sense and,further, that one who seeks a clear definition of the scope of theinvention protected by these letters patent should have reference to theclaims which follow.

I claim:

1. A compact sewage treatment apparatus comprising: (a) a tank; (b)means for conveying effluent to said tank; (c) a primary effluentreceiving and holding chamber in said tank, said means of clause (b)being disposed to discharge effluent into the substantially mostupstream region of said primary chamber wherein heavier solids in theeffluent settle out of solution and biological decomposition of theeffluent by anerobic micro-organisms takes place, said primary chamberhaving means defining an extended length tortuous path downstream ofsaid region through which partially clarified liquid flows responsive tothe filling of the said region of said chamber with additional settlingof solid particulates and continued anerobic decomposition of theeffluent occurring during flow downstream through said tortuous path;(d) filtering means located in said tank downstream of said meansdefining said tortuous path, said filtering means being adapted toinhibit the passage of larger particulate matter in the partiallyclarified effluent downstream thereof and thereby retain said matter insaid primary holding chamber for further anerobicdecomposition of same;(e) a chemical treatment chamber located in said tank downstream of saidfiltering means for the reception of still further clarified effluentpassed through said filtering means,

1 wherein said last mentioned effluent is chemically treated by anappropriate chemical composition which reacts with organic materialpresent in the effluent to effect a reduction of coliforrn bacteria andbiological oxygen demand of the efiluent present in said chamber;

(f) means for receiving still further clarified effluent discharged fromand flowing downstream of said chemical treatment chamber, said meansdefining an extended flow path which the effluent traverses subsequentto leaving said chemical treatment chamber to provide for still furtherseparation of solids and liquids during passage of the effluent alongsaid extended flow path; and (g) means communicating with the downstreamregion of said means. of clause (f) for discharging highly clarifiedeffluent from said apparatus.

2. A sewage treatment apparatus according to claim 1 wherein the lengthof said tank is appreciably greater than both its height and its width.

3. A sewage treatment apparatus according to claim 1 wherein the flow ofeffluent through said apparatus subsequent to its initial discharge intosaid primary holding chamber is induced solely by gravitational force.

4. A sewage treaunent apparatus according to claim 1 wherein said meansof clause (f), claim 1, comprises a plurality of substantially parallel,communicating settling and flotation chambers located substantiallyadjacent said chemical treatment chamber.

5. A sewage treatment apparatus according to claim 1 wherein saidfiltering means is disposed in the environment of the substantially mostclarified effluent flowing downstream of said means defining saidtortuous path, but upstream of said. chemical treatment chamber.

6. A sewage treatment apparatus according to claim 1 including meansconnected to said tank for periodically discharging an appropriatechemical composition into said chemical treatment chamber.

7. A sewage treatment apparatus according to claim 4 wherein saidprimary effluent receiving and holding chamber is located adjacent thebottom of said tank, said means providing said tortuous path is disposedabove the most substantially upstream region of said primary holdingchamber, said filtering means is disposed above said means providingsaid tortuous path, said chemical treatment chamber is disposed abovesaid filtering means, and said plurality of settling and flotationchambers are disposed substantially at the level of and longitudinallyadjacent said chemical treatment chamber.

8. A sewage treatment apparatus according to claim 7 wherein said meansdefining said tortuous path comprises a plurality of longitudinalbaffles spacedly super-imposed on one another and spaced above thebottom of said tank and extending substantially between the internalside walls and end walls of said tank, each of said baffles having anopening formed therein for the passage of effluent therethrough in adownstream direction, said openings being alternately locatedsubstantially at the opposite ends of adjacent baffles.

9. A sewage treatment apparatus according to claim 8 wherein saidbaffles are alternately, planarly inclined in opposite longitudinaldirections toward the bottom of said tank.

10. A sewage treatment apparatus according to claim 4 wherein saidfiltering means, said chemical treatment chamber and said flotation andsettling chambers constitute components of a separate subassembly havinga base disposed above said means defining said tortuous path, saidsubassembly being mounted within said tank below the top of said tankand in at least partially spaced relationship with respect to theinternal peripheral walls of said tank.

1 1. A sewage treatment apparatus according to claim wherein saidfiltering means is connected to the base of said subassembly by aconduit extending through an opening in said base and fixed to said baseand projecting downwardly from said base a predetermined distance towardsaid means defining said tortuous path, said filtering means being fixedto said conduit adjacent the lower most end thereof so as to lieappreciably below the base of said subassembly but above said meansdefining said tortuous path.

12. A sewage treatment apparatus according to claim 1 including asecondary effluent holding chamber disposed downstream of said filteringmeans and upstream, adjacent said chemical treatment chamber.

13. A sewage treatment apparatus according to claim 12 wherein saidsecondary effluent holding chamber is separated from said chemicaltreatment chamber by a transverse baffle having a length in excess ofone-half the width of said tank.

14. A sewage treatment apparatus according to claim 13 wherein saidtransverse baffle is imperforate and includes a section of reducedheight providing a weir facilitating downstream flow of effluent fromsaid secondary holding chamber into said chemical treatment chamberresponsive to the filling of the former.

15. A sewage treatment apparatus according to claim 1 wherein saidfiltering means of clause (d) of claim 1 comprises a plurality ofprimary enlarged, relatively coarse filters and said apparatusadditionally includes a plurality of secondary, relatively finer filterslocated downstream of said chemical treatment chamber.

16. An apparatus according to claim 15 wherein said plurality ofsecondary filters are disposed in a predeter mined sequence relative tothe path of flow of effluent downstream of said chemical treatmentchamber with the most upstream of said secondary filters being thecoarsest of the group and each successive filter disposed downstreamthereof being progressively finer than the preceding filter.

17-. A sewage treatment apparatus according to claim 10 wherein saidsettling and flotation chambers are separated from said chemicaltreatment chamber by a transverse baffle joined to the base of saidsubassembly and extending across the width thereof and upwardly towardthe top of said tank and said settling and flotation chambers aredefined by a plurality of spaced, vertical, longitudinally extendingbaffles joined to the said base and extending from the downstream wallof said transverse baffle to the end of said subassembly most remotefrom said chemical treatment chamber.

18. A sewage treatment apparatus according to claim 17 wherein saidtransverse baffle has at least one opening formed therein adjacent oneend thereof and adjacent the said base of said subassembly to providefor the egress of effluent from said chemical treatment chamber to themost upstream of said settling and flotation chambers, said openinghaving a filter overlying the u tream end thereof to inhibit the assa eof larger solid matter from said chemical trea ment chamber into thefirst of said settling and flotation chambers.

19. A sewage treatment apparatus according to claim 18 wherein each ofsaid longitudinal bafiles has at least one opening formed therein andeach of said openings has a filter overlying the upstream side thereof,said openings being alternately disposed adjacent the oppositelongitudinal ends of succeeding baffles and alternately adjacent theupper and lower regions of succeeding baffles to provide for saidextending flow path of the effluent downstream of said chemicaltreatment chamber and the settling and flotation of solid particulatematter out of solution in the effluent during passage of the effluentthrough said chamber toward said means of clause (g), claim 1.

20. A sewage treatment apparatus according to claim 19 wherein each ofsaid filters overlying said openings in said longitudinal bafiles isprogressively finer than the preceding filter in said series of filters.

21. A sewage treatment apparatus according to claim 19 including meansconnected to said tank for periodically injecting an additional amountof chemical into the effluent present in one of the intermediate of saidsettling and flotation chambers defining the said extended flow path toprovide for a concentrated chemical attack on any organic matterremaining in the already highly clarified effluent present in saidchamber and thereby effecting a further substantial reduction of thebiological demand of the oxygen present in the effluent prior todischarge from said apparatus.

1. A compact sewage treatment apparatus comprising: (a) a tank; (b)means for conveying effluent to said tank; (c) a primary effluentreceiving and holding chamber in said tank, said means of clause (b)being disposed to discharge effluent into the substantially mostupstream region of said primary chamber wherein heavier solids in theeffluent settle out of solution and biological decomposition of theeffluent by anerobic microorganisms takes place, said primary chamberhaving means defining an extended length tortuous path downstream ofsaid region through which partially clarified liquid flows responsive tothe filling of the said region of said chamber with additional settlingof solid particulates and continued anerobic decomposition of theeffluent occurring during flow downstream through said tortuous path;(d) filtering means located in said tank downstream of said meansdefining said tortuous path, said filtering means being adapted toinhibit the passage of larger particulate matter in the partiallyclarified effluent downstream thereof and thereby retain said matter insaid primary holding chamber for further anerobic decomposition of same;(e) a chemical treatment chamber located in said tank downstream of saidfiltering means for the reception of still further clarified effluentpassed through said filtering means, wherein said last mentionedeffluent is chemically treated by an appropriate chemiCal compositionwhich reacts with organic material present in the effluent to effect areduction of coliform bacteria and biological oxygen demand of theeffluent present in said chamber; (f) means for receiving still furtherclarified effluent discharged from and flowing downstream of saidchemical treatment chamber, said means defining an extended flow pathwhich the effluent traverses subsequent to leaving said chemicaltreatment chamber to provide for still further separation of solids andliquids during passage of the effluent along said extended flow path;and (g) means communicating with the downstream region of said means ofclause (f) for discharging highly clarified effluent from saidapparatus.
 2. A sewage treatment apparatus according to claim 1 whereinthe length of said tank is appreciably greater than both its height andits width.
 3. A sewage treatment apparatus according to claim 1 whereinthe flow of effluent through said apparatus subsequent to its initialdischarge into said primary holding chamber is induced solely bygravitational force.
 4. A sewage treatment apparatus according to claim1 wherein said means of clause (f), claim 1, comprises a plurality ofsubstantially parallel, communicating settling and flotation chamberslocated substantially adjacent said chemical treatment chamber.
 5. Asewage treatment apparatus according to claim 1 wherein said filteringmeans is disposed in the environment of the substantially most clarifiedeffluent flowing downstream of said means defining said tortuous path,but upstream of said chemical treatment chamber.
 6. A sewage treatmentapparatus according to claim 1 including means connected to said tankfor periodically discharging an appropriate chemical composition intosaid chemical treatment chamber.
 7. A sewage treatment apparatusaccording to claim 4 wherein said primary effluent receiving and holdingchamber is located adjacent the bottom of said tank, said meansproviding said tortuous path is disposed above the most substantiallyupstream region of said primary holding chamber, said filtering means isdisposed above said means providing said tortuous path, said chemicaltreatment chamber is disposed above said filtering means, and saidplurality of settling and flotation chambers are disposed substantiallyat the level of and longitudinally adjacent said chemical treatmentchamber.
 8. A sewage treatment apparatus according to claim 7 whereinsaid means defining said tortuous path comprises a plurality oflongitudinal baffles spacedly superimposed on one another and spacedabove the bottom of said tank and extending substantially between theinternal side walls and end walls of said tank, each of said baffleshaving an opening formed therein for the passage of effluenttherethrough in a downstream direction, said openings being alternatelylocated substantially at the opposite ends of adjacent baffles.
 9. Asewage treatment apparatus according to claim 8 wherein said baffles arealternately, planarly inclined in opposite longitudinal directionstoward the bottom of said tank.
 10. A sewage treatment apparatusaccording to claim 4 wherein said filtering means, said chemicaltreatment chamber and said flotation and settling chambers constitutecomponents of a separate subassembly having a base disposed above saidmeans defining said tortuous path, said subassembly being mounted withinsaid tank below the top of said tank and in at least partially spacedrelationship with respect to the internal peripheral walls of said tank.11. A sewage treatment apparatus according to claim 10 wherein saidfiltering means is connected to the base of said subassembly by aconduit extending through an opening in said base and fixed to said baseand projecting downwardly from said base a predetermined distance towardsaid means defining said tortuous path, said filtering means being fixedto said conduit adjacent the lower most end thereof so as to lieappreciably below the base of said subassembly but above said meansdefining said tortuous path.
 12. A sewage treatment apparatus accordingto claim 1 including a secondary effluent holding chamber disposeddownstream of said filtering means and upstream, adjacent said chemicaltreatment chamber.
 13. A sewage treatment apparatus according to claim12 wherein said secondary effluent holding chamber is separated fromsaid chemical treatment chamber by a transverse baffle having a lengthin excess of one-half the width of said tank.
 14. A sewage treatmentapparatus according to claim 13 wherein said transverse baffle isimperforate and includes a section of reduced height providing a weirfacilitating downstream flow of effluent from said secondary holdingchamber into said chemical treatment chamber responsive to the fillingof the former.
 15. A sewage treatment apparatus according to claim 1wherein said filtering means of clause (d) of claim 1 comprises aplurality of primary enlarged, relatively coarse filters and saidapparatus additionally includes a plurality of secondary, relativelyfiner filters located downstream of said chemical treatment chamber. 16.An apparatus according to claim 15 wherein said plurality of secondaryfilters are disposed in a predetermined sequence relative to the path offlow of effluent downstream of said chemical treatment chamber with themost upstream of said secondary filters being the coarsest of the groupand each successive filter disposed downstream thereof beingprogressively finer than the preceding filter.
 17. A sewage treatmentapparatus according to claim 10 wherein said settling and flotationchambers are separated from said chemical treatment chamber by atransverse baffle joined to the base of said subassembly and extendingacross the width thereof and upwardly toward the top of said tank andsaid settling and flotation chambers are defined by a plurality ofspaced, vertical, longitudinally extending baffles joined to the saidbase and extending from the downstream wall of said transverse baffle tothe end of said subassembly most remote from said chemical treatmentchamber.
 18. A sewage treatment apparatus according to claim 17 whereinsaid transverse baffle has at least one opening formed therein adjacentone end thereof and adjacent the said base of said subassembly toprovide for the egress of effluent from said chemical treatment chamberto the most upstream of said settling and flotation chambers, saidopening having a filter overlying the upstream end thereof to inhibitthe passage of larger solid matter from said chemical treatment chamberinto the first of said settling and flotation chambers.
 19. A sewagetreatment apparatus according to claim 18 wherein each of saidlongitudinal baffles has at least one opening formed therein and each ofsaid openings has a filter overlying the upstream side thereof, saidopenings being alternately disposed adjacent the opposite longitudinalends of succeeding baffles and alternately adjacent the upper and lowerregions of succeeding baffles to provide for said extending flow path ofthe effluent downstream of said chemical treatment chamber and thesettling and flotation of solid particulate matter out of solution inthe effluent during passage of the effluent through said chamber towardsaid means of clause (g), claim
 1. 20. A sewage treatment apparatusaccording to claim 19 wherein each of said filters overlying saidopenings in said longitudinal baffles is progressively finer than thepreceding filter in said series of filters.
 21. A sewage treatmentapparatus according to claim 19 including means connected to said tankfor periodically injecting an additional amount of chemical into theeffluent present in one of the intermediate of said settling andflotation chambers defining the said extended flow path to provide for aconcentrated chemical attack on any organic matter remaining in thealready highly clarified effluent present in said chamber and therebyeffecting a further substantial reductIon of the biological demand ofthe oxygen present in the effluent prior to discharge from saidapparatus.